marky, good point regarding the MBM being down firing on carpet. I guess it depends on the carpet and padding materials as far as what frequency range and how much acoustic energy is absorbed ??

I have hardwood flooring in my listening room and can tell you a lot of energy gets transferred to the floor with the MBM volume set at about 55%. My guess is that if you loose some energy on carpet that you can compensate by simply increasing the MBM volume a tad ??

Stone; earlier in this thread I covered MBM grounding. The MBM has a 2 prong power cord (no third ground prong) so it is not really grounded. I think HSU does this to avoid ground loop issues that can crop up from plugging equipment into multiple home power outlets that have less than ideal common grounding.

Early on I discussed a hum that I had with Dr. Hsu and he explained they expected virtually everyone to use the line level input connections into the MBM. I gathered from our conversation that HSU relies on the line level interconnect ground lead back to the power amp to serve as the MBM ground back to the power amp ground (common ground).

Since I have my MBM's connected via speaker level connection there is no ground to the power outlet (two prong power cord) or the amp other than the speaker wires back toe the power amp. This created a slight hum at the main speakers. I eliminated the hum by connecting a jumper wire with alligator clips on each end from one of the MBM toggle switches to the case on the surge protector where my amp and other equipment are connected and grounded.

The ground hum I encountered could only be heard at close range and then it was faint (with cd player on pause). But when I finally grounded the MBM to the surge protector it really cleaned things up further during music playback.

The ground loop was laying down 60 Hz noise that the MBM, mains or both were reproducing (amplifying) during music playback. It was similar to a 60 Hz room induced peak, could only turn Up the MBM volume so much before the peak started to make things a bit boomy. Grounded the MBM plate amp to the surge protector everything else was connected to and I was able to increase the MBM volume further with no more tendency to get boomy.

You can get a package of four 3 foot jumpers at Radio Shack for about 5 bucks.

DBC, thanks, I do have a low level faint hum at close range and I will get some Alligator Clips from R-Shack. (Using Spkr level conn too).

I love what I'm hearing from the MBM. The unit on carpet has no issues. I have it set at 150 hz and in sealed mode just a line under half volume for my room. I have it 5 feet out from the right corner wall-along the wall far enough away from me not to cause localization.

This is not a Subwoofer for sure! The MBM overlays so well in this hertz range. It is tuned to be articulate (fast) and subjectively dances along in tune with those upper mid bass lines. It thus, helps present an even larger soundstage with that little more weight I was craving (and at low to medium volumes)!

HSU markets the MBM for HT. The MBM needs to be sold to 2 channel music lovers with Tube Amps! Other than figuring out your placement....it does not need a long break in (you know when you hook this thing up/it has the Mojo IMHO)...even though it should benefit from that over time too.

Just a quick word on fit and finish. I ordered the Rosenut. The unit has bull nose corners like the sheet rock in my house....absolutely beautiful. The Bash Amp is recessed/routered in....very nice. The cone is a paper pulp triple surround bellow....like a Pro Eminence Driver of sorts. It exudes....I'm fast bitch! hehe...not a Subwoofer/thick excursion.

Thanks DBC for bringing your experience with this product to the Forum.The augmentation I'm geting with my CKC with MBM; for 625 bucks delivered is a steal. -Stone

My reaction upon first listen to the MBM in my system was right on with yours. You can probably now appreciate that my words can in no way do this device justice, you simply have to hear one in your system. I'm glad you had the balls to go out on a limb on this and give one a try.

You are right, HSU is missing the whole 2-Channel music market. And yes for the price The MBM is an absolute steal !!

The good news is that as you experiment it will only get better. The MBM has so much low end resolution it will immediately tell you when you are making improvements with placement, cables, grounding, vibration control, etc. Each time you make an improvement you will be able to bump up the MBM volume just a tad for more expansive and cleaner bass.

We had a winter storm here in the Midwest this weekend so I had a good bit of time for music listening. Got on a Santana Kick and was just mesmerized at how great the bass lines are in his music with the Mid Bass Module. HSU has been manufacturing the MBM for years and I just can't figure out why it is such a "Best Kept Secret" in music circles ???

Ok, I do have to say that HSU Marketing is a bit of a turn-off to 2-channel music listeners following in the "Less Is More" tradition. HSU talks primarily about HT applications, crossovers and near field placement. Believe me it's not that complicated for quality 2-channel listening. Just place the MBM somewhere between the mains, make speaker level connections, set the MBM crossover to 150 Hz (max position) and gradually increase the volume until you get the correct amount of magic.

Anyway as I listened to Santana I surfed with my tablet for any mention of the Mid Bass Module on the many audio related sites out there. Over the past 6 or more years every once in a while someone will ask "Anyone know anything about the HSU Mid Bass Module, they sound interesting?". Overwhelming the responses are from experienced subwoofer owners with a multitude of seemingly reasonable explanations as to why the MBM is a bad idea and all the technical reasons why they just will not work. Interestingly however, everyone kind enough to offer their hard and fast subwoofer Do's and Don'ts has never actually heard the HSU Mid Bass Module ???? So generally the person asking the question fades into obscurity as the well meaning experts pile on.

While surfing I found this Mid Bass Module review that some may find interesting: See link to full review.

"Forget about bass response in your current primaries for a bit. Put them where they work the best for mid-band and highs, imaging, depth of field, and such. THEN, slowly bring up the Hsu mid-bass module(s) reinforcement volume until you find the sound growing fleshy and substantial, and you can clearly hear bass lines (which now are actually resolved into musical events, instead of an indistinct "tock-tock").

Because the units are light paper, they are very fast and you get virtually no hang or "tubby" sound; Crisp, clean, articulate and tonally correct.

On one of my most-favorite songs, "Sultans of Swing," by Dire Straits, suddenly the bass line was as clear and intricate as Mark's guitar licks. Wowzers!

In other words, you get what you wanted from "audiophile mid-bass," but you also get music with substance."

Guess I'm a sub nerd ?? I go to live shows locally a couple times a month (Blues, Rock, Pop) and use those listening experiences as a guide to what I would hope to achieve in my listening room. Over 20 years I have tried many subs, multiple subs, parametric equalizers, digital signal processing, room treatments, all with limited success at best.

So I thought I knew a lot about the subject and was not very optimistic when I purchased the HSU Mid Bass Module. I ordered it anyway thinking I might learn something and gain some insight to carry me forward in my quest. Well what I learned was I didn't know squat. It was as if I thought the Bass world was flat and suddenly I was having to wrap my brain around the fact that the world was actually round.

Stone_Of_Tone recently purchased a Mid Bass Module and his initial report was very positive. He has only had it a few days but I look forward to hearing more from him as he applies it in a different system and different room.

I used to think that a sub volume remote was a must in a music system. The ability to nudge the sub volume up or down depending on the music material. Sometimes even between songs on the same disk.

I have not touched the volume control on the MBM in over a month while playing a wide variety of music. It just makes everything sound right as rain.

"Ok, I do have to say that HSU Marketing is a bit of a turn-off to 2-channel music listeners following in the "Less Is More" tradition. HSU talks primarily about HT applications, crossovers and near field placement. Believe me it's not that complicated for quality 2-channel listening. Just place the MBM somewhere between the mains, make speaker level connections, set the MBM crossover to 150 Hz (max position) and gradually increase the volume until you get the correct amount of magic".

Five days in for me and you said it best DBC (above).....the MBM augmentation is real and musical for me too.

Many people can't wrap their brains around a 2 watt Amp driving Speakers either....their loss to ignorance as well.

People question me driving my Polk LS-90's with 2 watts per channel (or less actually per channel because of loss in the Xover)....but sitting 5 feet away and listening at 78db SPL average....the tone and texture I'm getting is amazing with a Decware SE84CS & Super Zen CKC. NOW, with the MBM....this System is complete.

However, sure more efficient Speaker's would let me go Louder....so I just nogotiated a price on a pair of Klipsch RF-7 II B stock in Black from Mike at Acoustic Sound Design. DBC, you have been happy with yours and I like what I heard from a little pair of RF 52 II's.....so I have the RF-7 II's coming!

Of course, I will be getting the MBM out to the HT & Bedroom Systems and report back. I will also get the RF-7 II's into the Listening Room (after burnin') to go head to head with my Polk LS-90's at 78db avg. SPL for Tone & Timbre comparisons.

beowulf, I can't answer that question with absolute certainty since I'm running full range mains. My guess is it might have even a greater positive impact with smaller speakers? Most Bookshelf speakers today have output down to 50-60 Hz and the MBM simply lays over or augments the 50 150 Hz range.

In my system the MBM meshes seamlessly producing a much broader more solid foundation to the music. It just adds dynamics and snap to drums and bass notes that you do not get from speakers alone. This carries throughout my house and sounds good in any of my rooms and I'm talking at only low to moderate volume.

I've been listening at lower overall volumes with much more satisfaction than ever before. The problem has always been I keep nudging the volume up looking for the BEEF and typically things get edgy before the BEEF arrives so I have to back off the volume and settle for what I can get. With the MBM the perfect amount of BEEF always seems to be there regardless of volume.

The MBM-12 is connected to the Super Zen via speaker level connection also operating in what HSU calls "Augmentation Mode". So the mains and MBM-12 are both reproducing the signal below 150 Hz down to around 50 Hz. ........

Per Steve Deckert's advice I use the speaker level connections so that the MBM is reproducing as close as it can the signature of the Super Zen amp. ........

So left channel for instance I run speaker level connection to the left sub and daisy chain to the left MBM.

Sorry for my ignorance, but I am confused by speaker level connection. I guess your amp has only one set of binding posts out...Are you running two wires off each speaker out post?

This is fun thread. I, like many, have spent a lot of time, money and struggle with this 150 or so down frequency range. I have it sounding exceptional now, and I am beginning with more power (Torii MkIII) and my speakers (HR-1) go low easily and well....but...you know...this thread makes me wonder.

With this room, there is no place between my speakers for an MBM, so I am thinking it may not work for me...

Stone: How is your placement exploration going?

Do you guys think it may be possible for a single unit to work outside the speakers. I sort of doubt it. When I had a Veladyne sub years ago, even it, with a lower crossover, sounded better between the speakers, though it was still good much closer to one than the other.

I am wondering if it might be worth the trial thing knowing it would have to be placed outside the main speakers.

Lon, thanks....this MBM is fun and worth trying when you're ready. Meaning: I know you are moving to help your folks and I wish you a good move and a not so arduous set up to your new surroundings and Listening Room.

Will, the answer is yes, two sets of wires off of the amp left and right speaker posts. I use Kimber between the amp and Speakers. I use Cat-5 network cable between the amp and Mid Bass Module.

The Mid Bass Module has a very high input impedance which means it draws virtually no current from the amp so the small Cat-5 conductors work just fine. For a Single MBM I have used a single Cat-5 cable which has 4 twisted pair. I strip back the insulation and twist conductors together to effectively have two twisted pair (left plus & minus, right plus & minus). So basically you end up with one contained cable that carries the left and right signals and it is good for longer runs (especially when experimenting with multiple locations). I prefer the Cat-5 with solid conductors, they seem more durable.

As far as placement I have only tried it once outside the speakers. Placing the MBM in the front right corner in my room resulted in a 60-70 Hz room induced peak. This was a room issue unrelated to the MBM best I can tell. In a different room it may have been fine ??? So in all honesty I can't answer that question. I can say using a single MBM located next to my right speaker sounded good (it does not sound like the bass is weighted to the right side of the soundstage at all).

It's interesting and maybe Stone can share his thoughts here but with the MBM pretty much anywhere along my front wall I can never actually hear IT. All I hear is the improvement it adds to the overall music presentation, no audible directionality. It very well could be fine as long as it is not directly beside or behind your listening position.

In general I have found the MBM to be very forgiving as far as placement and integration into the rest of the system. Nowhere near the issues that regular subwoofers seem to always present.

Yeah I'm moving alright, was packing a POD today. I really don't feel I need these MBM in my current set up with the HR-1 speakers predominantly played, those have a lot of mid-bass energy and a solid lower foundation, and this room has enough volume to get some good waves going. Wondering about my next place, and also about playback levels there, and won't know for a while (and predict a lot less listening time so even if it may be "needed" it may not become a priority).

Yes the Jupiter caps! Amazing in my newly modded...also a way to get weight and body...Zstage. I wanted another input and the Jupiter caps and Steve did these with a ground update. My Zstage is #02.

Right off the caps sounded notably better to me than my memory of the stock caps, more information (especially in the upper mids, but throughout) and better flow without sounding too anything. Now with a few more days on them, things are getting more smooth and sweet. Though the bass is quite good, no doubt the caps will continue to get better, and as usual, become more resolving. I look forward to how they end up sounding.

Anyway "riding the gains" is back for me, and I really like this tool for adding or subtracting weight and body depending on the recording and volume.

Oops, I forgot to thank you for your input on MBM placement and hookup clarification DBC. I do appreciate your careful and informative observations! Looks like it could be worth a try here...A bit of a crap shoot with the room mode based on placement thing you have mentioned, and since my options are very limited, but hmmmm...I have to consider it more.

I see you are out New Mexico way so shipping charges from CA to you would not be that bad. I would encourage you to give it a try. Get a 15 foot length of Cat-5 cable off the roll at Lowes. Hook up the MBM as suggested and with this length connection you can experiment with it around the room at various locations. Although you know it can't stay there try it in front of you somewhere between the mains for comparison also. This thing does not need to be slam up against a wall to be effective.

I have to warn you though, the Mid Bass Module is a bit like Indoor Plumbing, once you have experienced it you probably won't want to send it back.

I received a new Canned Heat CD today (Future Blues 1970) and was listening to that during lunch. My toes were tapping and head was bobbing to the rambling Blues Jam with a great bass groove. Half way through the CD I turned the Mid Bass Module and HSU 15" sealed sub OFF. WOW, what a let-down. I could still hear the bass line but it was thin and not engaging at all compared to what I was just listening to.

Next I turned the 15" sealed sub back ON (crossed over at 50 Hz). Really not much improvement, still dry. Flip the MBM back on and my toes are tapping and head is bobbing once again.

DBC,Will, the answer is yes, two sets of wires off of the amp left and right speaker posts. I use Kimber between the amp and Speakers. I use Cat-5 network cable between the amp and Mid Bass Module.

The Mid Bass Module has a very high input impedance which means it draws virtually no current from the amp so the small Cat-5 conductors work just fine. For a Single MBM I have used a single Cat-5 cable which has 4 twisted pair. I strip back the insulation and twist conductors together to effectively have two twisted pair (left plus & minus, right plus & minus). So basically you end up with one contained cable that carries the left and right signals and it is good for longer runs (especially when experimenting with multiple locations). I prefer the Cat-5 with solid conductors, they seem more durable.

Hi DBC, is there any way you can snap a pic of the back of the amp of how the cables are attached? I'm trying to picture this in my mind, but a pic would be really helpful of possible!

So are both cables (speaker and cat) screwed into the same speaker binding posts on the amp? How are the speaker cables terminated (with spades, bananas or with just the raw cable)?

My apologies, I can see I was not clear regarding the connections and appreciate your pointing that out. I generally use bare wire connections so multiple wires connected to a binding post is not a problem. I can see that for many that is not the norm.

A little background. About 10 years ago I purchased a set of Kimber cables with banana connectors. Tried them in my system 3 or 4 times over a 2 year period and never warmed up to them. They just sounded Dark with no Sparkle on the high end. Then one day for the hell of it I removed the banana ends and installed them bare end. A completely different cable and been using them ever since. So based on that experience I generally go bare wire to eliminate the connector as a possible variable.

If you happen to use spades then you can get stackable banana connectors from Radio Shack that will accept bare ends from the Cat-5 cable:

These will plug directly into the top of the existing Decware binding post. These are the ones I use when experimenting and a lot of plugging and unplugging is required.

If you are using speaker cables with banana terminations then you should be able to attach bare end wires to the Decware binding post and it will still accept the banana connectors from your speaker cables.

For the MBM I use CAT-5 network cable simply because it is designed to carry low level electrical signals while rejecting electromagnetic noise. The MBM has a big Magnet & Coil in it. I don't have any engineering data to support that it actually works in an audio system but to my ear it sounds good on the MBM.

DBC, thanks, I do have a low level faint hum at close range and I will get some Alligator Clips from R-Shack. (Using Spkr level conn too).

I love what I'm hearing from the MBM. The unit on carpet has no issues. I have it set at 150 hz and in sealed mode just a line under half volume for my room. I have it 5 feet out from the right corner wall-along the wall far enough away from me not to cause localization.

Stone, just wondering how your system is coming along?

Thought I would mention that in my room with two Mid Bass Modules I have the volume knob set 2 lines above half volume on each. Initially I could not set the volume above half or else it would start to get a little boomy on some music but not other. Music that went really low could get boomy.

For anyone following this thread, the Mid Bass Module volume knob has 20 lines etched into it. So adjusting the knob setting up or down by one line is not much in terms of knob rotation but has quite an effect on the perceived MBM output from my experience.

When I upgraded to the CKC I was able to increase the MBM volume to 1 line past half volume due to it's improved low frequency resolution. Later after improving the MBM ground the volume was increased to 2 lines past half volume. I should mention that each time I was able to increase the volume setting the bass did not really get louder, just cleaner.

Now I can listen to all types of music with no tendency to get boomy. If I turn the MBM volume up to 3 lines past half volume it does not get boomy, rather just sounds like there is too much bass. To me this is an indication that the MBM frequency response is now reasonably flat in my room.

My point here is if you sense a boomy tendency on some music material but not other with a given MBM volume setting then you could potentially have an issue with:

Source component low frequency resolution is lacking.

Amp low frequency resolution should not be an issue since we both have the CKC.

Room induced low frequency peak due to MBM placement.

Low frequency peak created by 60 Hz AC hum due to ground.

Stone, another point. I was concerned about wiring between the amp and MBM. If you run these wires close to power cables they may pick up induced AC noise, also the MBM is not magnetically shielded. That is why I went with CAT-5 computer cable.

Although I was impressed with the MBM performance out of the box, it took months before I realized some of these little issues existed in my system. They were subtle but addressing them made a difference.

Klipsch RF-7 II's are in the House (bedroom System)/since Wednesday. Man, these Spks were something to schleep in by myself from the garage unpacking. I am home today, so I have about 20 hours on them since Wednesday night.

My MBM 12 is out in the 2.1CH HT setup. I am liking it very much in this capacity placed behind the couch with the regular Sub up between the mains. Movies, Vinyl, Sat. Radio and LIVE at Daryl's HOUSE from Palladia are awesome. I did not care for the MBM in my Listening Room System. I prefer the purity of the SuperZen CKC in that; my Reference System.

Back to the Klipsch RF-7 II's: I purchased a pair for $1780.00 delivered factory brand new B Stock (I found one little scratch that rendered it B Stock). Audio Design out of Las Vegas/Factory Auth. Dealer/Mike Embers...I highly recommend. I received great service and a great product shipped timely via R & L Carriers on a skid/pallet.

I had to work my Alchemy on the best mix of Equip & Cables...I ended up running my Kimber Hero IC with the Zen Styx...also with my (2nd) AA DTI Pro, then into my Cambridge DAC Magic. The DTI Pro takes this DAC to another level...and is still signifcant today.

Anyway, the RF-7 II's blow the ZU Unions away. The Zu's came with 500 hours burn in and I only have 20 hours on the Klipsch. The Zu's could not get the upper treble right for me. I guess it is right to say for some of us....."I have never found a 10" full range driver with a whizzer cone I've liked".....even one crossed over at 12K. YMMV

Any designer including Steve will tell you....one System can't do it all....SO I have 4 System's. I have the subtle Tone/Texture and layering musicality in my Listening Room Reference System.I have the brute force and extra loudness when called upon with the RF-7 II's. ....yes, I have already freaked out my neighbor with just 2 watts running the RF-7 II's.

I had to do it. I moved the Klipsch RF-7 II's to my 2.1.1 Rig (w/MBM 12 & Velo Sub). You can drive them with 2 watts/ch as DBC can attest to. However, boy do they love power! .....running off my Emotiva XPA-2. I am going to enjoy them in this Rig for awhile and then get them in to the Listening Room eventually (they are big and heavy when moving them by yourself)...along with the return of the MBM 12.

I put the RF-52 II's back in the Bedroom System to stay. They do a nice job in this BRoom Rig setup. Cheers, Stone

The RF-7 II's spent Monday & Tuesday night in the 2.1.1 Rig for some Solid State Action with my Emotiva XPA-2 = Fun. However, late last night it was time already to hand the Torch back to my Polk SRS SDA 1.2's with the Emo Amp and HSU MBM 12. So I moved them in to the Listening Room System and the RF-7's are lets say, high efficiency Speakers I can live with.

The 7's can't layer Tone and Decay of notes, or provide the sense of Air around the Instruments as well as my Polk LS-90's can with my Kimber Select 1030 IC and Kimber Select 3033 Speaker Cable with SuperZen CKC or SE84CS...but they are fun none- the-less for the extra volume, when I want to crank it up a little more! I have each pair of Speakers configured in the room to not hurt the other sonically and I can switch Speakers via my Banana Plugs between the Pairs on the Fly.

The RF-7's certainly benefit from No Negative Feedback and Even Order Harmonic's. Like Paul Klipsch said: "what the world needs is a good 7 watt Tube Amplifier". Steve D certainly makes them from 2 to now 60 watt Mono Blocks. (I prefer the Original Svetlana SV83 Pentode's run in Triode with No Negative Feedback...Steve is Genius for capitalizing on this Tube).

My Listening Room size and Acoustic Treatments are yeilding good Bass from the 7's. I am not inclined to bring the MBM 12 back in any time soon. I am loving what the MBM 12 is doing with my Sources in the Emotiva Rig with the SDA 1.2 Speakers.

Anyway, the MBM is a worth while Product and I use it most of the time in the Big Rig with the main Velo Sub off. It integrates very well and the Volume Knob is at my left hand reach to adjust for different Sources. Less is more with this wonderful Mid-Bass device.

Cheers, Stone of Tone (off now to put gas in the Snow Blower for my pending 6 to 8 inches we are to receive today...Spring/what Spring?)

Thanks for this review DBC. I find it ironic there is so little in the way of reviews on the MBM-12. I added a pair near-field behind the couch to compliment my pair of Hsu VTF-2 MK3 subs up front. Amazing difference in performance, especially in music performance. Thanks again for taking the time to write this up, its one of the few reviews for these MBMs.

Glad to hear that your MBM-12 purchase is adding so much to the enjoyment of your system. You nailed it, these are great with Home Theater but what they do with music has to be heard to be believed.

Based on your equipment list I guess you have the MBM-12's connected via line level (interconnect) connections?? I was just wondering if you have any detectable hum from the MBM's when music is on pause?? Also was curious where you have the volume knob set on each unit.

I have my MBM's connected via speaker level connections and in the beginning had the volume knob set at about 35%, any higher and the bass would get a little boomy. Took me a while to realize I had a ground loop and low level 60 hz hum creating the boomy effect.

I was able to cure the ground loop, get rid of the 60 hz hum and increase the MBM volume setting to 50% with very positive effects. Just thought I would mention this in case you have any detectable hum.

In any event in my conversations with Dr. Hsu he indicated the potential for ground loops (60 hz AC hum) is minimal when using line level connections. Just wanted to confirm your method of connection and that it is hum free.

Yes the Yamaha 3010 processor has dual independent low level sub outputs and thats what Im using for both the subs and MBMs. The outputs are split and the Yammy is set for a front/rear sub configuration. Good phase was a priority for me and luckily YPAO got my distances very accurate, especially considering Im running a pair off each output. Crossover from satellites to low levels are higher than Ive ever preferred but after much experimenting with 80 Hz I found that 90 Hz just works better. The VTFs take over at 45 Hz to prevent phasing and reinforcement as much as possible.

My gain is really determined by YPAO. Both subs and MBMs are well below 25%, like 15%, otherwise YPAO would come back during room calibration and say the gain is too high and it cant lower them enough. Im hyper sensitive to localization and yet even near field with a 90 Hz crossover I get no localization and excellent performance. Sounds very natural, mellow and with no boom at all, very hard to argue with what YPAO does in the gain department. However I can see running a higher gain if they were far field along my front stage. Luckily Ive never had any buzzing. I listen to my system pretty loud with both music and theater so I think Im good, free of any ground loop issues, thanks for the heads up.

This my first post to the forum and my first venture into stereo gear in a long time. I purchased a SE341.3 amp, Decware speaker cables/interconnects, Denon turntable, Oppo BPD105, HSU MBM12-MK2, and a soon to arrive pair of MG944's to play it all through. I have not heard any of my system yet. I have been connecting all of my components as they arrive and the last piece was the HSU MBM12. I am using some Straight Wire double shielded cables running from the line out jacks on the amp to the MBM and am getting a low hum from the module when it is powered up without the amp being turned on (haven't powered it up at all not having speakers yet). I tried plugging the MBM directly into the wall and through my surge protector with no difference. Powering it up without the line cables plugged in I get no hum at all so it is not an internal issue with the module as far as I can tell. The HSU paperwork says it is a grounding issue withe interconnects or the amp. Any ideas as to how to solve this would be welcome. I read earlier in this post of some similar issues when using multiple subs and modules but this may be a different scenario. I am truly excited to hear all of the promise that this system holds just need to get it right. Thanks from a newbie

They come in a 4-pack so you can clip them together to create a single longer lead as required.

Clip one end of the test lead on to any of the toggle switches on your MBM amp. Clip the other end of the test lead on to the case of the surge protector that you have all your other gear connected to. This will connect the chassis of your MBM amp to the same earth ground as everything else in your system.

If your surge protector is properly grounded, then the MBM chassis will be on the same earth ground as all your other equipment and this should eliminate the hum. Not the most elegant solution but it is very effective.

If you have the MBM power cord connected to a surge protector be sure you are using one of the "High Current Outlets" on the surge protector. The MBM needs a good bit of juice since it has a 350 watt internal amp.

You probably noticed the HSU MBM has a 2-prong power cord (no earth ground). I discussed this curious choice with Dr. Hsu. My understanding is they went this way to minimize Hum issues associated with Poor Earth Ground Wiring found in many homes. If your home wiring does not have a good ground to earth to begin with then refrigerators and other appliances can feed electrical noise back into your system through the earth ground.

Bottom line is if you want a completely Hum Free (Ground Loop Free) audio system you have to have a home that is properly wired to earth ground to begin with. Second, to eliminate any potential Ground Loop between components within your audio system each component chassis must be properly connected to the same earth ground. Connecting the ground jumper as I outline above should do that.

Shold350, Sorry for the confusion. I have three audio surge protection strips and all three have metal housings (cases). The metal housing is connected to earth ground per the electrical schematic provided in the owners manual.

If your surge protection strip has an all plastic outer housing clipping the MBM ground jumper wire to the plastic will not establish a path to earth ground. If your surge protection strip has threaded coax connectors for cable surge protection (see photo) clipping to the threaded outer portion will work also. In the photo the green jumper wire from MBM toggle switch is connected to the surge strip via the outer threaded portion of the coax connector.

The ground post of any unused receptacle will work also but I don't think you will be able to clip to it ??

Thanks for the images. I changed my connection from the line outs to the MBM to using the speaker posts going to the MBM and the hum is all but gone. I can hear it only if I turn the volume up almost to max on the MBM. I'm still not sure how it will sound when it gets a real signal from the amp. Thanks again for all of your help with this

DBC,I'm not sure of the date for the mains but it should be fairly soon. My only concern is that I am having to place the mbm to one side of my couch which is the only seating in my bedroom converted to a small media/listening room. I just don't have enough wall space with my setup to put it out in front with the mains. I hope that with some volume adjustments through the dual controls on the amp and the one on the mbm I can find a good compromise. I am sure it will still sound better than any thing I've had since an old rack mounted Nikko setup I had back in 1979 running a pair of JBL L-36's.

I received the MG944's a few days ago and have been playing with the system as much as possible. Overall I am blow away by the quality of all of the components in my system. It is by far the nicest system I have ever owned and I am just getting started on the break-in period.

I have run into what seems to be somewhat of a common problem however. I am getting some pretty noticeable hum. I only have two sources coming from my Decware input selector box into the amp. One is a Denon turntable and the other is an Oppo 105 BDP. When I remove the interconnects from the Oppo the hum is eliminated. All of my components are run through a low dollar surge protector which is going into a standard wall socket. I have tried switching plugs around. Moving the Oppo/Amp off of the surge protector individually and plugging them directly into the wall with no change in the hum (didn't really expect to make a difference). I don't have the budget to have a special circuit created just for this room or the buy any exotic type of power conditioner. Any suggestions as to a reasonable remedy would be welcomed. I have a Rachel amp and have read in the forum that their may be a difference in the grounding on these compared to other Decware amps. I am no engineer and don't know if this actually accurate just trying to get it quiet. I have also noticed that dvd soundtracks do not play as loud as music cd's. Having to turn up the volume to play some concert dvd's just makes the humming a larger problem. I spoke to Steve about this issue and he has sent me some 6N2P input tubes to bump up the gain. I will try to post some pics of my new system over the next few days.

I have the Oppo BDP-83SE, DVD's & Blue Ray's typically have lower output levels than CD's (have to turn the volume knob up as you describe). No hum in my system with higher volume settings.

Is the Hum coming primarily from your main speakers, mid bass module or both? Any 60 hz hum from a ground loop would become more audible as you increase the MBM volume knob setting.

Since hum disappears when removing the Oppo interconnects it sounds like a ground loop between the Oppo and Amp. This suggests the Amp power cord and Oppo power cord are not seeing the same clean connection to earth ground when plugged in? Say for example the power cord earth ground connection on the Oppo is not as good as the power cord earth ground connection on your Amp. What happens is that any AC in the Oppo chassis (that would normally flow harmlessly to ground through the Oppo power cord) instead finds an easier path to ground through the interconnects and Amp power cord.

First thing I would do is go Oppo Direct to Amp, Amp to Mains and mid bass module turned OFF. If hum is still present disconnect speaker level connections to the mid bass module to eliminate it entirely. If hum persists try connecting a test lead from the Amp chassis to wall socket earth ground. Do the same for the Oppo if necessary.

Found this simple, crude but effective diagram on the net to help visualize ground loops. In this case two devices (amp & mixer) are connected to two different outlets going to separate breaker panels each with it's own earth ground rod. The power cord from each device has 3 conductors (Hot, Ground & Earth Ground).

In this case the the earth ground connected to the mixer has a potential of +3 volts while the amp earth ground is at 0 volts. Electrons always wanting to take the path of least resistance travel from the mixer across the audio line connection to the Amp and to Earth Ground through it's power cord.

The same problem can also occur even if Amp & Mixer are plugged into the same power strip. If power strip outlets have differing resistances to earth ground the same loop will occur. Current will flow over the audio line connection to the device with the best earth ground connection.

As a test you might try clipping one end of a test lead to the chassis of your Amp and the other end of the test lead to the chassis of your Oppo. This will provide an alternative path (between amp & oppo) for the current and will generally reduce hum if a ground loop exists. If hum is reduced it does not solve the problem but confirms a ground loop between two devices as the problem.

In the example above the ground loop would be eliminated if both devices were connected to the same ground (either one). Differences in resistance to earth ground can be caused by poor internal grounding within inexpensive power strips, poor wall outlet connections, improperly grounded wall outlets etc. For the time being I would remove any power strips and connect both devices into the same wall outlet. If the hum still exists check the wall outlet wiring & earth ground. If plugs fit loosely into the wall socket replace the wall outlet.

DBC, Thanks for all of your help on this. I am modifying my home built stand tonight and will be putting the system back together tomorrow. It will give me a chance to try some of the tips that you have given me. The hum is not noticeable when any music is on but having to turn up the volume quite a bit on some concert dvd's it is noticeable between songs. Might be too picky? Just want to get the best out of what is truly a nice sounding setup. I have about 15 to 20 hours playing time on the system and it is starting to open up I think. I am relocating my MBM from a side location to the front. This is requiring a modification to my stand but it sounds much better in the front.If you have some tips as to posting pics on the new user forum I would like to try some. Thanks again for the advice and by the way it was your comments on the MBM that made me buy one. It was truly the icing on the cake.

Because of the low output of my DVD players I ended up getting my CSP2 and then my now three CSP2+ preamps. They really solved THAT problem, and added to the system too with weight and tonal balance that is "just right."

You are not being too picky. For comparison this morning I was playing J. Joplin on my Oppo. I hit Pause and turned the volume knob on my Super Zen all the way UP. I had to have my ear very close to the main speaker drivers to hear only the faintest of hum.

I strongly recommend you get a quality surge protection device to plug all your equipment into such as this affordable unit from Tripp Lite:

Down the road you might want to consider an Isolation Transformer for your source components. This is basically the same unit Decware uses for their equipment demos and was recommended to me by Steve Deckert:

I don't think an Isolation Transformer will solve your ground loop issue. These are used primarily to filter out noise on the incoming AC line that can induce hiss, static and hum into your source components.

If you use the Tripp Lite Isobar plug everything into that so each piece of equipment is on the same ground. The Mid Bass Module has a 2-prong plug (no earth ground) so I suggest clipping one end of a test lead to one of the MBM toggle switches and the other end to the metal case of the Isobar. This grounds the MBM amp chassis to the same ground as your other equipment.

If you do have a ground loop (60 hz hum) the MBM is very capable of making that audible. If you don't solve the Hum issue then you will only be able to set the MBM volume knob at about 30% (any higher and the bass gets boomy because of the 60 hz peak created by the ground loop). Once I solved my ground loop issue I was able to set the MBM volume at 50% with no boomy tendency. I have not touched the volume knob on my MBM for over a year now.

You are right about placement of the MBM for music. Sounds best along the front wall somewhere between the mains for best imaging when using a single MBM. Should note that once I solved my ground loop my MBM was not sensitive to placement anywhere between the mains.

DBCI ordered the TripLite surge protector today. Even if it does not cure the hum issue it looks like a good investment for protection. Thanks for the referral. LonI have hopes of adding a CSP pre amp to my system someday. It will have to wait a while. I could always try to present the argument to my wife that the new surge protector will have one slot left empty on my current setup which could result an unbalanced line situation and could cause some serious damage to large investment we have made. It would be unwise not to get the CSP as another layer of protection. Unfortunately she is very intelligent and I would have no chance.

Yeah, I know all about having to explain and justify things to a wife. That held my system back for a long time, and when I lost her to lymphoma and MDS my system was able to grow and bloom in ways it probably never could with her around.

Still I'd rather have a boombox and VHS recorder than not have her if I had that choice! So hold your wife close and always tell her you love her!

when I lost her to lymphoma and MDS my system was able to grow and bloom in ways it probably never could with her around.

That is probably one of the weirdest things I've ever read in any online forums, anywhere.

I'm sorry for your loss, Lon. It really sounds like you've been through a lot. - I don't think Brianne could handle any more love and kisses from me, I'm pretty sure I smother her as it is. But it's sound advice my friend.

I was just curious as to any progress you may have made since your last post a couple weeks ago?

I was also interested in your impressions of the Oppo BDP-105 on music. I run the older BDP-83SE (Special Edition) directly into my Zen (no pre-amp). Have used the Decware CSP2 a couple of times but prefer the sound of my Oppo directly into the Zen amp.

DBC,I guess it's been about 3 months since purchase.Yes, major difference.Like I said before the room sucks for sound.18ft. ceiling 12ft.wide 32ft.long sloping down to one end.System is super zen.Oppo bdp95 ,MG945 speakers.The sweet spot in this room was at the far end from my setup,sounded fabulous there.But I don't want to stand at one end of the room to listen to music.So enter the bass mod.It sets right next to the MG's and is connected as per your instructions from the zen.I can sit anywhere in the room now and enjoy the music as it should be.Truly amazing the information that is in the upper low end,and this system is also used for home theatre.I'm not really a sub-woofer kinda guy,don't need explosions to rattle the house, the mid bass covers enough low end for movies and fills in nicely for the music.I like the fact that you can dial in the freq. although I generally keep it at 150hz and volume set at half.Seems to work fine for most everything.Now since it's down firing into the carpet this concerned me a bit.I placed it on a board but that didn't seem to make a difference,I may experiment with that more in the future.By the way,thanx for turning me on to this.Phil

Wanted to add that placing a Sub Dude II isolation platform under my Mid Bass Modules and Sub Dude HT under my Subs really made a difference. I have a wood floor and was amazed how much energy was being transferred into the floor via the MBM & Sub enclosure feet. The floor was acting like a big radiator.

Did not think it possible to improve Bass & Mid Bass further but the isolation platforms made a very noticeable improvement (better clarity, even smoother bass). For the price I highly recommend the Auralex product on any suspended floor (carpeted or not).